In wireless telecommunication systems, the design of data transmission is a challenging task. The data transmission may be impaired by several factors, such as fast and slow fading, interference from other systems and interference from other users within the same system.
Different methods have been developed against these impairments. These methods include the use of diversity in the transmission and reception and interleaving of a signal. When diversity is used, more than one transmission path is utilized between a transmitter and a receiver. In systems employing WCDMA (Wideband Code Division Multiple Access), multipath propagation is used as a diversity method. In diversity methods, information contained in a plurality of received signals that do not correlate with one another is combined. In WCDMA multipath reception, diversity signals are combined after despreading.
In a typical radio channel between a transmitter and a receiver, errors occur in bursts, in other words they are unevenly distributed in time domain. This is the reason for using interleaving, which aims at changing the bursty errors caused by a channel to separate errors independent of each other. In systems where a signal is transmitted in frame format, interleaving may be realized in a transmitter by rearranging the bits in the frame so that long error bursts can be randomized when deinterleaving is performed in a receiver.
One problem with interleaving is the usage of memory. In many WCDMA receiver implementations, the output of a diversity combiner is usually stored in a buffer memory. After all symbols of a frame have been received and stored in the buffer memory, a deinterleaving unit reads the buffer memory, and stores a deinterleaved frame in another buffer memory. The realization of multiple buffers after diversity combiner increases the size of an integrated circuit used in the implementation of base band parts of a WCDMA receiver. In addition, processing delays in the receiver are increased.